Adrenocorticotrophic hormone causes an increase in cortisol, but not parathyroid hormone, in dogs

Dogs with spontaneous disorders of glucocorticoid production often have marked disturbances in calcium homeostasis. For example, hypercalcaemia is frequently observed in dogs with hypoadrenocorticism and secondary hyperparathyroidism is a common feature of canine hyperadrenocorticism. The mechanism(s) by which glucocorticoids modulate calcium homeostasis in dogs remains ill-defined. The hypothesis of this study is that a marked increase in serum cortisol concentrations would lead to an immediate negative calcium balance state which would drive a compensatory increase in parathyroid hormone (PTH) concentrations. This hypothesis was investigated by measuring serum cortisol and plasma PTH concentration in 19 dogs before and after administration of adrenocorticotrophic (ACTH) hormone. Post ACTH administration, there was a significant increase in serum cortisol, but not PTH, concentrations. The results of this study do not support the hypothesis that an increase in endogenous glucocorticoids influences calcium balance sufficiently to cause an immediate, compensatory increase in parathyroid hormone concentration.